An LED is a two-lead semiconductor light source having a p-n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching.
LEDs are electronically controlled using a device called a “driver” (also known as a “regulator”, “converter”, “light engine”, and other similar terms describing the same device), which generally function by providing either a constant current or constant voltage to the LED. These drivers are typically set up in a straightforward manner to ensure the proper current and voltage drives the LED. If the forward voltage of the LED is higher than the voltage of the power source, a “Boost” or “Step-Up” driver is used, and if the forward voltage of the LED is lower than then voltage of the power source, a “Buck” or “Step-Down” driver is used. Other driver topologies including but not limited to “Buck-Boost”, “Charge Pumps”, “Linear Drivers”, “Cúk”, and other types are used for the purpose of controlling LED brightness. LEDs may be composed of single colors or multiple colors.
Drivers may be single mode, multi-mode, or fully-variable, depending on the control arrangement. They may be controlled in an analog manner, or via a digital control arrangement using a microcontroller or similar device.
A single topology driver is typically used to control the LED within an LED flashlight. Even if the LED flashlight has a variable brightness control, the control for brightness is often located on the same single driver topology that drives the flashlight itself.
Turning to FIG. 1, shown is a prior art schematic 10 with a single driver 12 driving a single LED or LED array 14. As shown in FIG. 2, these prior art devices have only one specific point of maximum efficiency, which the design must be optimized to meet. Graph 20 shows an example efficiency plot for such a single driver. As seen from graph 20, the exemplary single driver achieves 94% efficiency at 350 mA of current but only has 40% efficiency at 10 mA of current. For any point outside of this point of maximum efficiency, the effective battery life of a portable electronic device (such as a flashlight), is reduced, sometimes greatly.
There are many deficiencies to this solution, namely:
1) A single-chip or single-topology driver can generally only control a single LED or LED array.
2) As shown in FIG. 2, a single driver has a specific point of maximum efficiency, which the design must be optimized to meet. For any point outside of this point of maximum efficiency, the effective battery life of an portable electronic device (such as a flashlight), is reduced, sometimes greatly.
Accordingly there is a need for an improved design of LED-based flashlights to improve efficiency and battery life.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.